Liver is one of the body's most important organs. It has a complex structure and performs a variety of physiological functions. Acute or chronic liver disease, especially liver failure, has a severe impact on human health. Liver transplantation is a unique and effective approach to treat patients with end-stage liver disease or liver failure. However, its application is greatly limited by the scarcity of donors, the graft failure and the need for long-term use of immunosuppressive agents. Therefore, there remains a need for an alternative approach for treating serious liver diseases. Liver tissue engineering holds promise for the treatment of serious liver diseases.
Tissue engineering has emerged as a new cross-disciplinary field since late 1980s. In recent years, with the development of life science and materials science and engineering, breakthroughs have been achieved in in vitro reconstruction of a variety of tissues and organs, and some of tissue engineered products such as cartilage and skin have now been commercialized. Liver tissue represents an important research direction in tissue engineering. The ultimate goal is to construct a transplantable liver tissue or organ to treat patients with impaired liver function. Liver functions as a plant of the body where chemical synthesis, detoxification, biotransformation, and nutrition processing occur; it is also a place where the complex body supplies adjustment takes place. The tissue structure and physiological functions of the liver are complicated. The liver consists of a myriad of functional units called lobules. The lobule is composed of hepatocytes, bile capillaries, and sinusoids. Through these basic functional units, the liver performs a variety of functions including metabolism, nutrition and excretion of bile. How to construct a fully functional or transplantable tissue engineered liver in vitro remains a major challenge in the liver tissue engineering.
Bioreactor is a key component of a bioartificial liver, at which the material exchange between exogenous hepatocytes and patient's blood or plasma takes place. However, to date, progress in the development of bioreactor has been slow. Materials currently used in bioreactors as well as design configuration and efficacy of bioreactors are far below the desired level. Accordingly, how to design a structure so that bioreactors can more closely mimic the tissue structure of a normal liver, thus providing a living and metabolic environment similar to an in vivo environment for the cultivation of hepatocytes, becomes the most difficult part of future research. As to several types of bioreactors being developed such as flat plate bioreactors, hollow fiber bioreactors, microcapsule suspension bioreactors, and scaffold perfusion bioreactors, configurations of these bioreactors are quite different from the structure of the human liver. These bioreactors do not contain a bile excretion system and suffer low material exchange efficiencies. Therefore, there remains a need to develop new materials as well as an improved bioreactor design, so that the fluid mechanics and geometry of the bioreactor more closely mimic the physiological states. There are no bioreactors in the art having a hepatic lobule-like structure.